Patent GB-814597-A (GB)
Title: Improvements in or relating to telephone systems
Inventor: DAVISON ALAN
IPC: H04Q3/52
Filed: 1956-04-28
Abstract: 814,597. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. April 16, 1957 [April 28, 1956], No. 13096/56. Class 40 (4). Two sources of pulses having different characteristics are provided in common to all subscribers' line circuits and on the conduction of a set of static switching devices to extend the conversational and control paths from a subscriber's line circuit, one or other of said sources according as to whether said line circuit is in an originating or a terminating condition is connected to one of the conducting devices of said set so as to effect controls appropriate to the different conditions of the line circuit. Reference is made to Specifications 728,382 and 735,635 as examples of prior art. General arrangement. In a 100-line P.A.X. the line circuits SLC have access to 10 link circuits. Each line circuit is associated with 10 sets of tubes SP, H and P, each set extending to a different link circuit. Lines are scanned according to the tens and units digits and when a calling line is detected a set of tubes SP, H and P is fired to connect it to a pre-allotted link circuit. Originating negative pulses ONP and terminating negative pulses TNP are applied to each line circuit without effect until the line circuit is taken into use. When a line is calling the originating negative pulses are repeated over the operative P tube to a gate in the link circuit. Loop breaks in dialling interrupt these pulses to indicate the dialled digit to the register. A persistent break in the pulses indicates that the calling subscriber has hung up to cause the link circuit to generate a B pulse to release the connection. The terminating negative pulses TNP are concerned with indicating that the called subscriber has answered so as to cut off ringing. Marking of the called line circuit is effected by the register taken into use by marking leads TX, TY corresponding to the required tens and units digits to fire a set of tubes SP, H, and P in a multiple connecting the called line to the link circuit to which the calling line is already connected. The link circuit and register allotters LCA (not shown) and RA operate on a cyclic basis. When the pre-allotted link circuit LC1, say, is seized by a calling line circuit a two-conductor path is established to the pre-allotted register over a pair of tubes C1, D1 or C2, D2 according to the register concerned. The C tube is concerned with transmission of dialled digits to the register and the D tube with transmission of control signals from the register to the link circuit. These control signals indicate the condition of the register in setting up the call and are registered in sequence control counters RSCC and LSCC in the register and link circuit respectively. The register includes two cold-cathode counters TDC, UDC for storing the tens and units digits, respectively. When storage is complete the register sequence control counter RSCC determines that the fast scanner shall be extended from its normal 12 stages to 18 stages, the extra stages having no scanning function but providing distinct time periods for the two registers. In one of these periods the register marks the called line circuit. The fast scanner then reverts to normal operation. When an idle called line circuit is marked it causes the common control equipment to produce a Z pulse to release the register which then signals the link sequence control circuit LSCC whereby the called subscriber is rung under the control of pulses applied to the H tube. Ringing is tripped by an F pulse when the called subscriber answers. If the wanted line is busy no Z pulse is produced and after a short delay the link circuit returns busy tone and releases the register. The link circuit allotter LCA (Fig. 11, not shown) comprises a known type of counter which pre-allots the next idle link circuit. Link circuit. One link circuit LC1 is shown in Figs. 2-5. It includes a link sequence control counter LSCC comprising counting tubes FR, ALL-BY, controlled in known manner by pulse repeater tubes such as LPRI. FR conducts when the circuit is idle and unallotted, ALL when it is pre-allotted and SZ when the link circuit has just been taken into use. When ALL fires it causes MS, Fig. 2, to strike to the next P1 pulse to provide anode potential to the P and H tubes and cathode potential to the SP tubes in the 100 sets of multiple tubes corresponding to the 100 subscribers, while PPH, Fig. 5, conducts during each high-speed scanning cycle to cause the P and H tubes to be primed. Then when a calling line circuit is scanned a Z pulse on lead ZP, Fig. 3, is applied to all the link circuits to fire LPR4 momentarily in the allotted link circuit only. LPR4 shifts the counter to SZ conducting. Register allotter RA, Fig. 8. R1 or R2 conducts according to whether register REG1 or REG2 is pre-allotted, so priming C1, Fig. 2, or C2 in each of the ten link circuits. Assuming that the first register is pre-allotted, when a link circuit is taken into use its tube C1 fires. If both registers are in use separate C1 and C2 in two link circuits are conducting so that RR1 and RR2, Fig. 8, conduct alternately and VTBRB also conducts whereby R1 and R2 remain extinguished due to insufficient anode potential. Subscriber's line circuit and multiple. The function of each SP tube in the multiple, Fig. 1, is to complete a single-conductor speech path between a line circuit and a link circuit over transformers TRA and TRB. The H and P tubes are used for signalling and control purposes. When a subscriber initiates a call LT fires each time the ten line circuits having the same units digit are pulsed on lead Y by the fast scanner FS, Figs. 6 and 7. LT pulses the trigger of XYO which is primed by the low speed scanner SS, Fig. 6, over lead X according to the tens digit. When, therefore, the line circuit is scanned co-ordinately by both the fast and slow scanners XYO fires to the pulsed source PHT 1 to fire OT which is primed by the mark on lead X. LCG5 then conducts to back off LCG6, leaving LCG7 to repeat originating negative pulses on lead ONP to the cathodes of the ten P tubes in the multiple associated with the line circuit. XYO also pulses the trigger electrodes of the associated ten pairs of P and H tubes, only that pair relevant to both the pre-allotted link circuit and the calling line circuit being fired. A two-conductor path is thereby established to the link circuit. The fired P tube controls a guard circuit and the H tube fires the related speech tube SP. The originating negative pulses are now extended over tubes LCG7 and P to the cathode of LV5, Fig. 2, in the link circuit. Dialling. Each break in the loop backs off LCG7 so that 4 or 5 originating negative pulses are omitted. At each make 2 or 3 pulses are sent, while during the interdigital pause pulse transmission is continuous. As described later, these pulses are monitored by an originating pulse gate in the link circuit, the gate controlling the register. Called subscriber. According to the tens digit of the wanted subscriber the register applies a persistent mark to the TX lead of the appropriate ten line circuits. According to the units digit the register then pulses the TY lead of the ten line circuits having that units digit. If the wanted line circuit is idle LCG4 is fired by the TY pulse and ionises XYT. XYT fires TT, which primes ringing control tube RGC and busies the line circuit. XYT pulses the ten P and H tubes associated with the called line circuit. Tube LV3 in the link circuit primes the 100 pairs of P and H tubes in the multiple whereby the single pair of P and H tubes relevant to both the link circuit and the called line are fired. These strike the associated speech tube SP. With P fired the diodes LCG3 and LCG4 are backed off so that they are not affected by scanning or marking. Striking of XYT also causes generation of a Z pulse by the common control equipment. The Z pulse initiates release of the register which meanwhile causes the linkcircuit to send pulses over the fired H tube to the trigger of RGC, Fig. 1, to cause the called subscriber to be rung. When the called subscriber answers LCG6 repeats the terminating negative pulses on lead TNP over tube P to the link circuit to stop the application of pulses to tube H. Ringing therefore stops. If the called line is busy XYT does not strike and so there is no Z pulse and busy tone is returned, as described later, after a short delay. Line scanning. A fast scanner FS, Figs. 6-8, in the form of a cyclic counter normally has twelve stages F1-F12. It steps on one stage every 2 ¢ msecs. and produces pulses on leads Y1-Y10 which feed groups of line circuits having the same units digit. Each time the fast scanner reaches stage 1 it steps on the slow scanner SS which has ten stages and feeds leads X1-X10, each of which is connected to the line circuits having the same tens digit. When a register has stored the two digits of a wanted number RG7, Fig. 9, fires to cause SPR, Fig. 8, to fire when F12 in the fast scanner next strikes. SPR then switches in six extra stages F13-F18 of the fast scanner to provide pulses PHT4, PHT5 for use by the register in marking the wanted line. At the end of this cycle normal scanning resumes. While the extension is operative SPR fires SAP, Fig. 6, to cut off the marking of the X leads by the slow scanner, the slow scanner resuming with stage S1 when the extension is no longer operative. In the event of two subscribers with the same tens digit initiating calls simultaneously connection is established to the subscriber with the smaller unit digit, the Z pulse firing SAPA, Fig. 7, which disables the slow scanner so that the X lead in the second calling line circuit is no longer marked when tha appropriate units lead Y is scanned. At the end of the fast scanner cycle BRS10 restarts the slow scanner. Pulse generation. A control circuit CC, Figs. 12-14, produce